The present invention relates to a CATV (cable television) data transmission method in which data transmission is performed for groups of terminal units by addressing them with respective group addresses.
In a conventional CATV communication system, the central facility transmits data through an authorized channel to the terminal units which are provided for each subscriber. Each terminal unit has its own address, and is addressed to receive data through the authorized channel. If the system includes a large number of terminal units, then much time is required to poll all terminal units. This difficulty may be eliminated by assigning the same group address to a group of terminal units which use the same channel. That is, when a channel common to a group of terminal units is used to transmit data, then the group of terminal units can be addressed collectively.
For instance, as shown in FIG. 1, on the central facility side, that is, on the television signal transmitting side, a group address 1 and an individual address 2 are transmitted to a signal transmission control section 10, and then data 3 is transmitted. On the television signal receiving side, the address data transmitted from the central facility is applied to a group addresss comparator 4 where it is compared with the data in an individual addressing group address memory 5 assigned to the terminal unit. This is a comparison with the group address 1. Upon coincidence, an individual address comparator 7 is instructed to perform a comparison with the individual address. In the individual address comparator 7, comparison is made with the address in an individual address memory 8 assigned to the terminal unit. Upon coincidence with the individual address, a data processing operation is carried out in a data processing section 9. When the group address is not coincident with the data in the memory section, it is compared with the data of a group address memory 6 in the comparator 4. Upon coincidence, a data processing operation is carried out in the data processing section 9 so that the terminal unit can receive the television signal.
The above-described system is advantageous in that addressing each terminal unit can be achieved in a relatively short time compared with a polling system using individual addresses only. However, it is still disadvantageous in that viewing permission cannot be granted to a plurality of groups of terminal units. In other words, it is important in order to increase the degree of utilization for the subscriber that, where one terminal unit receives simultaneous transmission of common information, an optional group of terminal units can be selected.